texts: The energy density of DM (to be fluid,state parameter=-2)increases with time. Does it violate the concept of accelerating universe?

texts:
We know that dark energy with value of state parameter $\omega<-1$ is called phantom dark energy model. In this model if we assume dark energy to be a fluid with value of state parameter $\omega=-2$, we can say that the energy density of such dark matter increases with time.

My question is whether the above statement violates the concept of accelerating universe, because both the energy density and matter density turn out to be negative. If we use these values in the acceleration equation, we see the acceleration of the universe (second derivative of the scale factor) is negative.

My derivation is as follows. We have $\omega=-2$, so the equation of state is $p=-2\rho c^2$. From the fluid equation,
$$\dot{\rho}+\frac{3\dot{a}}{a} \left(\rho + \frac{p}{c^2} \right)=0\Rightarrow\rho\propto a^3$$
From the Friedman equations, $a=-k_1 t^{-2/3}$, so the energy density is $\varepsilon=\rho c^2=-kt^{-2}<0$. Hence the acceleration is
$$\ddot{a}=-\frac{4 \pi G}{3} \left(\rho + \frac{3p}{c^2} \right)=\frac{4 \pi G}{3} \times 5\rho = \frac{4 \pi G}{3c^2} 5\varepsilon$$ Since $\varepsilon <0$, this implies $\ddot{a}<0$.


texts:
What weather is present in Jupiter's great red spot?  Is it raining?  Is it snowing?  There is definitely a hurricane a blowing :-).  I know it is very cold, extremely high winds, has clouds of an orange / red color, and there is probably lightning.  I also know the gravity on Jupiter is strong, about 2.5x that of Earth.  Here is a similar question / answer that answers some of what I am looking for, but I still want to know if it is raining / snowing, etc...
What Would it Look Like Inside Jupiter's Great Red Spot?

I am making a level for Planetary Settlers that takes place in an air base trapped in the cloud tops of the Great Red Spot, and here is what I envision the red spot looking like so far (I am still working on adding the lightning): YouTube video of Jupiter Level Development.  I would like to know if I should add rain, snow, or any other unusual phenomenon present there.


texts: Why doesn't star size distribution conform to space rock size distribution?

texts:
The number of space rocks is exponentially related to the size of the rocks. There are more small space rocks than big ones. Stars are most commonly the size of the sun, big and smaller stars are rare, and giant stars are the rarest. Stars that are 0.5 solar masses should also be very bright and visible, but they are less numerous, when they should be more frequent than the sun.
What about planets? There should be many unaccompanied planets wandering in the darkness of space, without a star, and they should be a lot more common than stars themselves, becaues of the size distribution of space rocks and stars should be roughly parallel.
What am I missing?
graph of star size distribtion.
graph of space rock size distribution.


texts: What solar features would I see at 10x magnification?

texts:
I have a pair of binoculars with 10x magnification, 50mm objective diameter, and 6.5 degree (real) angular field of view.

I'm looking into buying solar filters for it (something like these) so I can view the sun. If I do so, will I be able to see most/many sunspots and planetary transits? Or is this simply not a powerful enough instrument to be worth investing in solar filters for it?

I like the idea of being able to check out the sun sometimes, but I don't know if I'm just getting way out of my league here and would need more complicated and expensive equipment to make it at all worthwhile. Thought I'd ask some experts before buying anything.


texts: Is it possible that a ultra-large portion of the space we live in is already inside a black hole? How could we refute this?

texts:
Trying to wrap my head around some concepts involving the very large gravitational fields of black holes, and what the gravitational gradients look like on a cosmic scale.

I'm familiar with the Great Attractor, and wondered if it were possible if the Milky Way and it's neighbors are already "doomed" to fall into whatever the anomaly is.

Per recommendation, I've moved the second half of my question to a new Question here: Assuming a sufficient amount of mass above the density threshold, does the actual concentration of the mass matter in creating a black hole?

Original Text:

  Extrapolating further, I've heard that the actual density of a black hole (within the volume of the event horizon) is pretty low, on the order of thin atmosphere - does that mean that any sufficiently large volume of mass over that density is also a black hole? Or does the actual concentration within the event horizon matter?


texts:
In class, we read a Scientific American article, "Cloudy with a Chance of Stars" that explained how the cores and the dust around them formed stars(he called them eggs for a chicken/egg analogy, where cores are eggs and I suppose novae are the chickens because the novae cause the core to start to collapse), but we don't know how the very first stars were actually formed.

What are the leading hypotheses in this area, or am I misinterpreting the article? If you have a Scientific American account, here's the article I am referring to.


texts: Why is the Earth's center still hot after millions of years?

texts: Why didn't the center of the earth cool after millions or billions of years? What keeps it hot?


texts: Determining North-South Line Via Watch Method: Theory & Reason

texts:
I recently read that if you're in the northern hemisphere and have an analog watch, then you can point the hour hand at the sun and know that a south line lies between (bisection) the hour hand and the 12 o'clock position:

Apparently the trick works in the southern hemisphere as well and needs to be adjusted for day-light saving (image taken from Wikipedia):

I would like to know the reasoning behind this trick, and would like to know if the trick can be applied to tell the approximate time provided I only have a Brunton compass.

I made an illustration if it helps:


texts: Where will I be able to see the Lyrid meteor shower?

texts: So supposedly the Lyrids meteor shower will take place between early morning April 16th to 22nd - correct me if I am wrong. I am aged 15 and am interested in skywatching, I just wondered will it be visible from the northern Hemisphere? Or will it be like the lunar eclipse and only be visible in the Western Hemisphere? Thanks.


texts: How to convert between AB and Vega magnitudes?

texts:
This might be a bit silly, but I'm really struggling with a conversion.
I have apparent AB magnitudes: $$m_{AB} = -2.5 \log_{10}(f_\nu [\mu Jy]) + 25$$ that I would like to convert to Vega magnitudes, because I am trying to make a figure similar to the one below from Stern et al. 2005. I used the conversions from this site: http://www.astronomy.ohio-state.edu/~martini/usefuldata.html, but it came out all wrong. Should I not use these? Because the axes contain colors, I suppose I don't have to worry about the units of $f_\nu$, because this will create an offset that cancels when you subtract two magnitudes, right? But I find that one color-conversion must be positive, because
$$[3.6]_{AB} - [4.5]_{AB} = [3.6]_{Vega} + 0.79 - [4.5]_{Vega} - (-0.09) \\= [3.6]_{Vega} - [4.5]_{Vega} + 0.88$$
while the other is negative, because
$$[5.8]_{AB} - [8.0]_{AB} = [5.8]_{Vega} +0.02 - [8.0]_{Vega} - 0.45\\
= [5.8]_{Vega} - [8.0]_{Vega} - 0.43$$
but if you look at this figure below, you see that you need two corrections with the same sign. Any thoughts on my attempt at conversion? Thank you.


texts: Which is the largest planet ever observed?

texts: I don't know much about planets outside our solar system. Do we even know the limit of the size of how large a planet or satellite can be? The largest planet I know of is Jupiter, but could there be planets as large as our Sun or even larger? Is there a theoretical limit to the size of a planet?


texts: Small changes to Earth's orbit caused by a large impact on the Moon

texts: Is there any scenario where a large impactor striking the far side of the Moon would perturb the Earth's orbit enough to reduce the distance from the Earth to the Sun and still remain within the habitable zone?


texts: Are the stars distributed in uniform distribution, on the celestial dome, with respect to brightness?

texts:
Has there ever been a statistical analysis of the distribution of stars in the sky (on the surface of the celstial dome), by brightness? I want to know if they are uniformly distributed.

For example, all stars with Apparent Magnitude from 1.0 to 2.0. Are these uniformly distributed? Then all stars from 2.0 to 3.0, etc.

EDIT: To avoid bias for the Milky Way, there should be some cutoff magnitude. I don't know exactly what's the best cutoff, but I would guess somewhere around 4.0 to 5.0 apparent magnitude. If the cutoff is 4.0, then that gives us 3 tiers to look at (1 to 2, 2 to 3, 3 to 4). Are each of those tiers uniformly distributed?

Btw, the "obvious" distribution of theta from 0 to 2pi and phi from 0 to pi will NOT produce a uniform distribution. That will produce clustering near the poles. Wolfram Alpha explains it.)

I did google around for this. The results are all about star clusters or binaries, not the actual starfield of the night sky, or sometimes about how to program a random set of stars on the sphere.

That's not what I want. I'm looking for a statistical analysis on our own starfield. Has it ever been done before? What were the results?


texts: As the Universe expands, do things like planets expand also, or just the space in between?

texts: Just what the question says. As the universe expands, and space expands, do objects like planets ever expand? Does the space INSIDE of those objects expand?


texts:
I was wondering if there were any available databases for photos of the night sky. It doesn't have to feature pictures of any particular star, just has to be a large collection of photos from the night sky. I would just go off google images, but those images are heavily biased in favor of exceptional views.

Preferably ones taken from ground level, like pictures of what would be visible to a normal person without equipment.


texts:
Consider black hole A, a super massive black hole at the center of the galaxy. Orbiting it is black hole B, a much less massive black hole.

If some passing body were to modify black hole B's orbit such that it fell within the Roche limit of black hole A, what would happen to black hole B?

If it were to turn into a ring, would the black hole matter re-inflate since it wouldn't be under such high gravity? Do black holes even respond to Roche limits like regular matter does?


texts: Limiting magnitudes for different telescopes

texts:
I live in an extremely light polluted place. On a new moon night,  magnitude 3.5 stars are at the limit of  naked eye visiblity on clear nights, and the Orion nebula is visible as a smudge through my binoculars and I can see 6-7 stars of the Pleaidies (apparent magnitude about 5.5 I guess)
If I buy a 130 mm reflector telescope, roughly what will be the limiting magnitude of the objects I can see?
I used $5log(130/6.5)=6.5$, which means I would be able to see upto about magnitude 10 even from a light polluted city.
This sounds too good to be true...
Is my estimate roughly accurate and do you think spending a few hundred dollars on the telescope is worth it if I never intend to leave the city for a while?


texts: Orbital eccentricity variation of the other planets?

texts:
On Earth, it's fairly well published, mostly in climate change related articles, that the Earth's orbital eccentricity operates on a 413,000 year cycle with roughly 90,000–125,000 year variation within that cycle.

Source

The cause of this variation is primarily the other planets, with Jupiter and Saturn usually mentioned as the primary causes (same link).

Question is two fold.   How stable is the Earth's orbital eccentricity cycle?  413,000 years sounds enormously precise, but logically, I would think small changes in planetary orbits would create some variability.   Is the 413,000 years well established and repeating or is it more uncertain?

And, do we have a good estimate of other planets orbital eccentricity variation?  I looked, but couldn't anything at all on other planets eccentricity cycles.   The closest I came was this gravity simulation chart below.

90,000 year eccentricity chart of the 4 inner planets here,
and method used.  Source.


texts: Would Hubble Space Telescope improve black hole image observed by EHT if it joined array of telesopes?

texts: My question is related to black hole image released in April. As far as I understand idea of EHT, it joins observations from multiple locations to work like one telescope with radius that is equal to the distance between the farthest telescopes in array. Moreover Earth atmosphere affects observation, e.g. by introducing delays. Would it beneficial to add Hubble Space Telescope to EHT and if yes, why HST was not included in observation array?


texts:
The smallest distance probed in any experiment so far conducted is $10^{-18}$m and the largest distance we can have is the radius of the universe, nearly $10^{26}$m. The ratio is $10^{44}$.

In another case, if we think about time, the shortest time studied is about $10^{-26}$ sec and the longest time is "the lifetime of the universe", which is estimated to be $13.7$ billion years, or nearly $10^{18}$ sec. The ratio is again $10^{44}$!

Is this(the ratio belongs is of same order) a coincidence or there is some deeper explanation(probably space and time are related etc.)? I am an undergrad student, don't know much about astronomy. I wondering about this question while studying quantum mechanics from the book The Quantum World, which claims that it is not a coincidence.

The book explains it in the following way -

"This is not a coincidence. The outermost regions of the universe are moving at a speed near the speed of light, and the particles flying about in the subatomic world are also moving at such speed. On both subatomic and cosmological frontiers, the speed of light is the natural link between distance and time measurements."

I haven't posted exactly what the book is saying because I wanted to hear what other people are saying about this and also because I haven't understood what the book is saying.


texts:
When is Earth closest to the Sun?

Well, you say, perihelion of course.  But perihelion is when the Earth-Moon barycentre is closest to the Sun. Not Earth itself.

The barycentre is on average 4,671 km from the Earth, which should mean that even if the orbit of the Earth-Moon barycentre around the Sun were perfectly circular, the Earth-Moon orbit around the barycentre would cause an oscillation in the Earth-Sun distance by twice that amount on a monthly basis.  That should be enough to move Earth's closest approach to the Sun away from perihelion.

Considering this, how many days from perihelion may Earth's closest approach to the Sun be?

Question inspired by: What place on Earth is closest to the Sun?


texts:
I am writing a 2D simulation for binary stars orbiting each other. Currently, the initial position of the stars are on opposite sides of the screen with the left star having a velocity up the page and the right star having an equivalent velocity down the page.
The question I have is there a formula for calculating what that initial speed should be so that the stars remain in a stable orbit? Optimally, the formula would take into account the mass of the stars (which are equivalent), the distance apart, and G.
My apologies if this question would be better directed elsewhere or if I overlooked the answer in my own research.
Thank you for your help.


texts: Why dimmer high-redshift supernovae means the expansion is accelerating, if the dilated region pertains the distant past?

texts:
I must be seeing this wrong, because it seems to me the data indicates faster expansion in the past, contrary to Adam Reiss' study that led to the birth of the notion of 'dark energy'.

In Reiss' seminal study, [https://arxiv.org/abs/astro-ph/9805201], which was followed by others [https://www.researchgate.net/publication/231060958_Measurements_of_O_and_L_from_42_High-Redshift_Supernovae] that confirmed the measurements (and earned him the 2011 Nobel), high redshift (very distant) Ia supernovae are 15-25% dimmer (i.e more distant) than the current Hubble constant (circa 74 km/s/megaparsec) would predict from their redshift. This lesser luminosity (or greater distance) in the distant region was concluded to signify the universe's expansion is accelerating, rather than slowing down as would be expected from the effect of gravity, as a ball thrown upwards by hand will rise more slowly each second until it stops rising and falls back down. Thus, that some effect must be accelerating the expansion of the universe, referred to by the placeholder name 'dark energy'.

This measurement generates a graph where low redshift (closer) supernovae seem to follow a straight line along the Hubble constant, and then in the more distant region the plot goes up from this straight line, as they are further than their redshift would predict, forming what I call for the purposes of this question a 'shallow V' shape.

[pages 267-269, How Old Is the Universe?, by David A. Weintraub, available at http://93.174.95.29/main/3FF82B0C945C31FF63E4388ED31AB7F9]

The standard answer is something along the line "The argument is pretty straightforward, and can easily be understood with a real-world example. Consider two cars leaving your house. They start out going at the same speed. But over time, one car speeds up, while the other slows down. After some time, which care will be farther away from you? The one that’s speeding up, of course. That’s obvious.  And something that’s farther away looks dimmer (at least if they have the same intrinsic brightness)."

This explanation - that the universe currently expands at a faster rate than in the past - does not seem to explain the “shallow V” curve we see. It would explain a “shallow A”, with a higher Hubble constant in the present and a lower one in the past. We see a curve (or a line with a bend on it) that - it seems to me - cannot be interpreted other than the greater increment being at the point of departure, most distant from us, not nearer to where we are, ie. with a higher Hubble constant in the distant past, say around 80-90 km/s/Mp.

How can we be seeing this curve we see with the accepted interpretation? Should not the curve be bending the other way? Obviously I must be seeing this wrong, but where is my error?


texts: How can we tell the age of a rogue planet?

texts: Is it possible to find out how old is a planet, especially a rogue planet? I know that people measured the radioactive decays to determine Earth's age with some amazing accuracy, but what about interstellar planets be, they gas or terrestrial?


texts:
The other night, I observed what I believe must have been a satellite, however it was at 1:30am so I was not sure that this would be possible. Being in the Southern Hemisphere we are just past Summer Solstice, so theoretically it could have been reflecting the sun's light.

There were no flashing lights, just a star-like point of light. As it slowly traveled in a NE direction across the sky, it began to gradually fade as typical of a satellite passing into Earth's shadow.

Based on my observation, I'd like to get an understanding of the approximate minimum altitude of the object that I observed, allowing for it to be out of the shadow of the Earth sunlight. I'm not a mathematician, but using Space Engine with the correct time & location, I had to position the camera to some 7000km in altitude before the sun was visible over the horizon. The object was N to NE from where I observed it, whist the midnight sun would have been shining away at the South Pole.

Date/Time: 27-Dec-2017, ~01:30 local time (GMT + 8)
Location of observation: Perth, Western Australia (~32S, 116E)
Position in sky : ~ 80 to 60 degrees elevation, moving north due northeast
Duration of observation : ~2 to 3 minutes


texts: How do you correct the Period-Luminosity relationship for metallicity?

texts:
Refer to the link: https://www.astro.utoronto.ca/DDO/research/cepheids/cepheids.html
Tha author has used the relationship $M_V=-2.902log(P)-1.203$. It is mentioned that this is not corrected for metallicity.
My question is how we could correct this for metallicity using SIMBAD $[Fe/H]$ values for individual stars, or otherwise using some other free & publicly available data.
I am open to suggestions.


texts: Is there a timeline for the naming of the TRAPPIST-1 worlds?

texts:
For the moment, the TRAPPIST-1 worlds are just known by their official designations, like "TRAPPIST-1a" etc. NASA made a casual tweet asking people what they would name the worlds, and there has been some talk of naming the worlds after Belgian beers due to the origin of the "Trappist" name, but I haven't heard any official talk about what names might be given to the new exoplanets.

I'm wondering, is there a timeline (either official or traditional) for the naming of these worlds? Based on previous names given to astronomical bodies, are they likely to have names within the year, or is it likely to take at least five years or something, or is it completely unpredictable?


texts: I know cosmic mean density for baryons is around $(2\ \mathrm{to}\ 5)\times10^{-31}\ \mathrm{g/cm^3}$, assuming that Hubble's Constant is $100\ \mathrm{km/s/Mpc}$. But what is the current cosmic mean density including all particles in the universe (dark matter etc.)?


texts: Could there be life beneath the surface of Mars or moons?

texts: I realize radiation and extreme temperatures would probably destroy life on the surface of most planets and moons, but could life exist beneath the surface (e.g. like earth worms on earth)?


texts:
How to make random positions in Equatorial coordinate system?

If I divide Dec between -90 and 90 evenly, the space distribution is not random.


texts:
In the wikipedia article for ephemeris time as first adopted in 1952, it does not explain clearly how or why it was superseded. For example, it reads:

In 1976 the IAU resolved that the theoretical basis for its current
(1952) standard of Ephemeris Time was non-relativistic, and that
therefore, beginning in 1984, Ephemeris Time would be replaced by two
relativistic timescales intended to constitute dynamical timescales:
Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time
(TDB).[28] Difficulties were recognized, which led to these being in
turn superseded in the 1990s by time scales Terrestrial Time (TT),
Geocentric Coordinate Time GCT(TCG) and Barycentric Coordinate Time
BCT(TCB). [16]

So, from this it appears that ephemeris time was never superseded and it continues to be evolved with a different theoretical basis?
From reading Robert Newton's books such as "Ancient planetary observations and the validity of ephemeris time", it would seem that ephemeris time is invalid because of non-secular accelerations in the motion of Mercury and Venus.
So, I guess my question is: does current astronomical theory consider ephemeris time to be invalid or valid, and if it considers it to be valid, then what is current evaluation of Newton's calculations and their implications for the validity of ephemeris time?


texts:
How do we weigh a planet?
My friend asked me how do scientists weigh a planet. He is not from science background so I need to make him understand with simple analogy. How can I explain to him?


texts: What will the last days of Earth be like?

texts:
The sun is a main-sequence star; as I understand it the sun will expand into a red giant in a few billion years.  I have heard conflicting reports of what this entails - some sources I found say the sun will expand until the current orbit of Earth is contained within it, others say it will stop expanding short of Earth's current orbit.

Every source has agreed that the planet will have long-since stopped being able to support life as we know it.

Assuming humanity takes no action to significantly alter the natural course of events, such as dramatic alterations of our atmosphere, what will the last few decades of Earth's life be like?  Will the planet be heated to the point where its surface is like Mercury's sun-side?  Will the sun's output drop low enough that it instead cools, like Mars?  Will the sun expand and engulf the planet, or will the planet continue to orbit an expanded sun as a lifeless ball?

Will the sun's expansion be gradual or rapid?  How will this expansion affect the rocky planets nearest to it?


texts: How can we predict a Big Crunch when all galaxies are moving further apart?

texts:
I've read that the further away a Galaxy is from us the faster it moves away.

By this logic how can scientists predict that there will eventually be a big crunch when every piece of matter is seemingly getting further and further apart?


texts: Celestron uncommon DC long barrel connector

texts:
I have tried to connect a 12v DC adaptor and also a battery pack to my telescope unsuccessfully. Sadly it seems Celestron DC jack needs to be around 2mm longer than common 5525 DC ports.
I was wondering what are those barrel connectors called so I can google it to find a male to male cable that is compatible.
And if Celestron is using an uncommon port to make customers buy its products or there is a technical reason for that?
Celestron DC5525 connector with ~14mm head.

Celestron DC5525 connector with 10mm head

I found this amazing illustration


texts: Which constellations are straight up and straight down?

texts:
Pretend you're in our galaxy near Earth and you're standing upright wrt the flat galactic disk.

If you look directly towards the center of the galaxy, that's Sagittarius. If you swivel your head and look directly away from the center, I believe that's around Auriga.

In fact, if you look straight up, about which constellation is that?  And if you look straight down?

(If I'm not mistaken, could be wrong, this is equivalent to asking about...

Wikipedia explanation of galactic coordinates

... galactic coordinates of longitude zero, latitude 90° (up overhead) and -90° (down through your feet).


texts: Does the axial tilt of Mercury and Venus vary?

texts:
The axial tilt of Mars varies greatly over time, with a tilt varying between 15 and 25° over the last million years, and varying even more over the last 5 million years. The Earth's tilt on the other hand is stabilized by the presence of a large Moon, so its tilt doesn't vary so much.
Venus and Mercury don't have any moons at all, so does their axial tilt also vary a lot over time? If not, why not? Do we have enough data to know how much their axial tilt has varied over time?


texts: How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?

texts:
According to quite recent research the observable universe contains about 2 trillion galaxies ($2 \cdot 10^{12}$). But what is counted there? Does this number also contain dwarf galaxies? According to wiki about 10 times more than normal galaxies exist. But is there a hard gap in between normal and dwarf galaxies?
To resolve all those questions does exist a chart or diagram similar to this?

Number of Stars
Count

$< 10^6$
$10^{11}$

$10^6 - 10^7$
$10^{10}$

$10^7 - 10^8$
$10^{9}$

...
...

bonus question:
As far as I know we are able to see new, more distant galaxies in the next millions of years. Due to the further expansion of the universe and the acceleration there will be some point were the light of some galaxies can't reach us anymore (hubble radius) and we can see less and less galaxies again. So the number of galaxies we can see is not a constant (also some get extinct or new are created). Is there some research about the max number of galaxies we are ever able to see. Would be it much different to the 2 trillion now?


texts: Are Wikipedia's sun ecliptic-coordinate formulae accurate?

texts: I'm creating a C++ program that calculates the ecliptic coordinates based on the formulae from Wikipedia But, my calculations appear off. The mean anomaly for today, for example, should be 80.4-something; both my program and Google calculate approx. 79.2 - the result of (357.528 + 0.9856003*5927) % 360 (where 5927 is the number of days since January 1, 2000, GMT)


texts: Precipitation and weather and seasons on other planets

texts:
I have participated in an exhibition on astronomy and decided to make a project on the topic "weather season and precipitation on other planets"

I have the knowledge about the weather on earth but I need to know more about that on other planets in the solar system like venus, mars, mercury and Jupiter etc or in other planets in the other galaxies.

Can anyone explain me how the precipitation and season  occurs,why do it occur, what is the effect,do they form clouds or something else,how do the temperature rotation and revolution affect the process? You can also suggest me some videos on this topic

Thanks in advance


texts: When did people discover that the Earth is not an ideal sphere, but a little flattened? And if you know, who was the first person to discover it?


texts: Could Mercury be the creator of Earth's Moon?

texts:
Earth's Moon is thought to have been created in a glancing collision with a Mars sized planet.

I've just seen an expose on Mercury which claimed Mercury: formed in the region between Earth and Jupiter, migrated to it's current orbit through an unknown interaction,  consist of 60% core material which was explained as the result of a glancing blow with a planet sized object.

Has anyone looked in to whether a Mercury/Earth collision could be the creator of our Moon?


texts:
ISRO's next mission to the Sun is Aditya-L1, (also here), which will be placed at the Sun-Earth Lagrangian point L-1.

Why it is not placed near L-4 or L-5, since these are stable equilibrium point whereas L-1 is unstable equilibrium? What is the advantage to placing Sun-observing satellites like Aditya near the L-1 point?


texts:
How old are Janus and Epimetheus, and are they believed to have formed out of a collision? (I think would explain their shared orbit).

Not the age of their elements, which should be similar to the age of the solar system, but the age of their surface and formation.

Cassini told us that Saturn's rings formed relatively recently, 100 or 200 million years ago.  Are there similar aging techniques that can be applied to the surface of icy moons and as that been done?   (related, this type of aging technique should apply to Pluto and Charon too, because they are believed to have formed by collision).

Edit:  I came across this which says:

  The extensive cratering indicates that Epimetheus must be quite old.
  Janus and Epimetheus may have formed from a disruption of a single
  parent to form co-orbital satellites, but if this is the case the
  disruption must have happened early in the history of the satellite
  system. From its very low density and relatively high albedo, it seems
  likely that Epimetheus is a very porous icy body.[4] There is a lot of
  uncertainty in these values, however, and so this remains to be
  confirmed.

So, significant uncertainty but probably quite old, early in the history of the satellite system, which would be fairly early in solar-system formation.  Much older than Saturn's rings.

I'll leave this question open in case anyone has better info, the above being from Wikipedia, though they reference a NASA article.


texts: What does a black hole elements consists of?

texts: What are the elements of a black hole it just says what a black hole is? There must be elements that the sun consists of, right?


texts: What has GAIA found out about the dwarf galaxy heritage of stars in the Milky Way, if anything?

texts:
I ran across the image below in the August 2000 ESA Bulletin # 103 GAIA – Unravelling the Origin and
Evolution of Our Galaxy

  Figure 3. This simulation shows how a galaxy halo, like our own, may have been
  built up by the accretion of 50 dwarf galaxies colliding with the galaxy at various
  times during the last 10 billion years. The unit of distance is the kpc, or kiloparsec, where 1 kpc is a little more than 3000 lightyears. GAIA would be able
  to detect the fossil streams of these ancient merging events (Courtesy of Paul Harding)

Twenty years later, have results from GAIA been used to generate any data of this nature, identifying groups of stars that are likely to have come from nearby dwarf galaxies merging with our own?


texts: Is there a limit to how hot a star can be?

texts:
I think that size and mass do not correlate to temperature, but then again these factors contribute to the internal pressure.

I would like to know if there is a limit to how hot a star can get and what mechanism(s) could drive a star to get unusually hot.

I also know that negative temperature occurs in laser is hotter than a positive temperature, and can a star produce negative temperature?


texts: Can electromagnetic waves be affected by gravity?

texts: Can electromagnetic waves change their properties in the presence of gravity?


texts: Do any known exoplanetary/solar bodies have "annular" eclipses similar to Earth's?

texts:
This was somewhat inspired by this question but is a bit different: I am interested in if there are any known systems in which the angular size of the eclipsing object is almost the same as the angular size of the object being eclipsed from the surface of a planet, as is the case for the Moon and the Sun as viewed from Earth. This is the only way that one can get "annular" eclipses, or eclipses in which the host star's corona is clearly visible. This could be the case for some moons in the solar system (which requires that they eclipse at all), and at least Phobos in particular seems to have a similar angular size to the Sun as viewed from Mars,

but it could also be true for some known (or candidate) multiple-planet exoplanetary systems in which the periods of the two planets are not too different. Probably a perusal of the public Kepler candidate sample would be helpful here.


texts: What would be the dynamics of a double-planet system, similar to Earth / Moon, but with both bodies nearly Earth-sized?

texts: Researching a sci-fi story involving a "twin-planet" system. Is such an arrangement (however unlikely) physically possible? And if so, must they be tidally locked with each other, similar to the moon, month-long days, etc?


texts: Why are event horizons described in Schwarzschild radii rather than diameters, and either way can they change equator to pole?

texts:
I never heard of Schwarzschild diameters, only of Schwarzschild radii. Why is it like this? Wouldn't it be better to portray the (possible) size of a black hole in a diameter?
Either way, can we use the terms radius or diameter term precisely? Is an event horizon always perfectly spherical or can it have something like an equatorial bulge even though it's a black hole's immaterial event horizon.


texts: Using SkyChoord to read in multiple coordinates.

texts:
so I recently wrote a basic code to analyze the distance between two points which are stored in two separate excel files. Now that I have that code working its time to apply the legitimate use and use this code to analyze not just 2 dimensions (x,y) but three (ra,dec,z). In the data sheets now I have stored the coordinates of two separate galaxies.  Heres the amended code below:

import math
import pandas
file1 = pandas.read_excel('Book1.xlsx')
file2 = pandas.read_excel('Book2.xlsx')
file1['RA_diff'] = file2['RA'] - file1['RA']
file1['DEC_diff'] = file2['DEC'] - file1['DEC']
file1['Z_diff'] = file2['Z'] - file1['Z']
dist = file1.apply(lambda row: math.hypot(row['RA_diff'], row['DEC_diff', row['Z_diff']]),   axis=1)
if dist.values >= .5:
    print 'no match'
elif dist.values <= .5:
    print True, dist

This code works great with just the RA and DEC but not no much with the Z added in.

My hope is that somebody please give me some pointers on how to shorten this whole process by using the method:

from astropy.coordinates import SkyCoord

Basically: How do I use this tool to my advantage in reading in (from two separate excel documents) two separate coordinates of (ra, dec, z) to determine if the objects have any proximity to one another?

My research has turned up rather fruitless to analyze the points in this way specifically as I mostly simply don't understand the help pages. This is my first ever coding project so please be gentle in your advice, recommendations, help, feedback or ANYTHING else you might be able to offer. Thanks in advance.


texts: I know all about how black holes form and why their gravity is so strong. However, is the gravity equally powerful in all directions? Will the event horizon appear as a perfect sphere?


texts: Can anyone calculate the distance the moon travels in a single year? I can calculate it as it is close to 2.4 million km, but I need adjustments as the earth is moving and so is the Sun. So, I need the absolute distance rather than distance from earth's perspective.


texts: Are we already moving faster than light?

texts: Okay, so the speed of revolution of earth around sun is 30 km/s[1], speed of revolution of sun around milky way's center is ~200 km/s[2], speed of rotation of milky way is 828,000 km/h[3] i.e. 230000 m/s. Since speed of light is 300000000 m/s, so on an even bigger scale (bigger than clusters) are we already moving faster than the speed of light? Or am I totally wrong?


texts: Do Noctilucent clouds cause problems with telescopes?

texts:
Noctilucent clouds are at around 85km altitude and are formed of ice crystals. The ISS recently posted a number of photographs of these clouds and pointed out the key feature, which is the bright blue glow.

Are these known to have an impact on ground-based or orbital telescopes?


texts: Will the "fabric of space time" rip from expansion?

texts: I'm quite familiar with the fabric of space time theory and as I've been quite lonely these past few weeks, I started thinking that since the universe is expanding and since the "fabric" is the universe, would our nice little sheet eventually rip and mess up space time?


texts: Do black hole singularities actually merge?

texts:
new questioner here so please be gentle.

Do the singularities of merging black holes actually merge together?  I mean there are 2 infinitely small objects (singularities) that are trying to find each other but for them to merge they have to join at the EXACT same point in space.  I know they can get close, but to expect them to align perfectly with zero tolerance seems impossible.


texts: Sun and moon's orbit in ecliptic coordinates using skyfield

texts: I am new to using skyfield, is there any doc or help file that can show me on how to get the orbit of Sun and moon in ecliptic coordinate for a particular date and time. This is a follow up question of this question


texts: Ephemeris data mismatch between Nasa Horizonz and Astro.com

texts:
I have tried to compare the Ephemeris data from Nasa's Horizons with ephemeris
tables from astro.com. And they do not match. Example:

Date: 22th of July 2018. Body: Mars. Time 00:00 UT
Horizons: 309 degrees (Ephemeris type=Observer)
Astro.com: 305 degrees (http://www.astro.com/swisseph/ae/2000/ae_2018.pdf)

But some bodies are matching. Like Mercury and Saturn.

Am I doing something wrong?

Sources:
Nasa Horizons: https://ssd.jpl.nasa.gov/horizons.cgi#top

Astro.com: http://www.astro.com/swisseph/swepha_e.htm


texts: What other definitions for a planet were proposed?

texts:
This article from the IAU states

The first draft proposal for the definition of a planet was debated vigorously by astronomers at the 2006 IAU General Assembly in Prague and a new version slowly took shape. This new version was more acceptable to the majority

What were the other proposals for the definition of a planet? What was changed between the first draft and the final version that was voted on?


texts: Magnitude, satellite flare and the Heavens Above app

texts:
On the Heavens above app for Android and maybe iOS, it shows negative magnitude values for Iridium satellites, but for other ones, it shows positive.  Here is a screenshot

Why is this?


texts: What is the intensity distribution of visible light over the solar disk?

texts:
What is the distribution of the visible spectrum over the solar disk?

Images of the Sun using the visible spectrum suggest that the light emmitted from the edge is almost equal to the light emmited from the center of the solar disk.

Is this correct and is there a scientific source that proves that? I was not able to find something citable.


texts: How to measure the altitude and azimuth of a star?

texts: Given that the star is crossing the local meridian line in a certain location, I've tried calculating the altitude of a star by finding the difference between the declination of the star and the latitude of the position from where it is observed (which I believe is not correct). I'm so confused about that and it would be of great help if someone could explain the altitude calculation. Also, I'm wondering how to calculate the position of a place (latitude and longitude) while the declination and the right ascension of a star at the zenith is known.


texts: Would it be possible to equip an asteroid to collect space junk in Earth's orbit?

texts: We all have heard about the problem with space junk in low earth orbit. NASA has a plan to put an asteroid in orbit around the moon. Would it be possible to equip propulsion systems onto an asteroid in order to maneuver it into an elliptical orbit around the earth, with the goal of collecting this junk?


texts: Are harmonic relationships among the rotation periods of the planets well known? Are they factors in other planetary phenomena?

texts:
Every 39.88 minutes 10 degrees ($\frac{360^\circ}{36}$) of arc passes over the zenith. It can also be stated that the 36th harmonic of the rotation period of the earth (1435.8 min) is equal to 39.88 min. Note the similar relationships with the rapidly rotating planets:

Mars, rotation period of $\frac{1477.2 min}{\text{harmonic of }37} = 39.92$
Jupiter: $\frac{595.8}{15} = 39.72$
Saturn: $\frac{639.6}{16} = 39.98$
Uranus: $\frac{1035}{26} = 39.81$
Neptune: $\frac{966.6}{24} = 40.28$

For the slowly rotating planets, and the Moon, the numbers are larger, but still very close to 39.88:

Mercury: $\frac{3520.2}{88} = 40.00 \text{     } (88 = 22 \cdot 4)$
Venus: $\frac{14582.4}{368} = 39.63 \text{     } (368 = 23 \cdot 16)$
Pluto: $\frac{9223.2}{232} = 39.76 \text{     } (232 = 29 \cdot 8)$
Moon: $\frac{39343.68}{992} = 39.66 \text{     } (992 = 31 \cdot 32)$

The questions are: Are these relationships well known? Are they factors in other planetary phenomena?


texts: Do telescopes harm while observing sun through them?

texts: I don't know whether we can observe a sun through a telescope. But if we can then will it harm our eyes and if such telescopes exists what is their configuration?


texts: I find the original reference seems to be here. I still do not understand the mechanism. It is necessarily occur in neutron binaries? Anyone can introduce it in detail? This paper is old.


texts: What was the orbital path of earth before collision with a Mars sized planet?

texts:
There are hypotheses about a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, about 20 to 100 million years after the solar system coalesced.

I guess this changed the orbital path of earth around the Sun. Do we have any info what was the Earth's orbital path before the collision? (I would prefer some visual explanation.)


texts: Original Hubble diagram units incorrect?

texts: Figure 1 from Hubble 1929 (original paper with open access pdf) has velocity with units of km. Is this just a typo or was there a reason the plot is printed this way?


texts:
Roughly how long did it use to take for the early Earth 4.5~ billion years ago to complete one revolution around the Sun?

(I know the Earth was spinning much faster, so a day would only take 2-3 hours, so I'd like to have the answer in terms of current Earth days for better understanding - if possible.)

(I Google'd the heck out of this question and couldn't find an answer.)


texts: If an event occurs at a point in space time what will an observer experience first, it's gravity or the light from it?

texts:
Let's assume a person is close enough to an object in space time to be able to observe it's gravitational effects and the light coming from it.
If that object suddenly pops out of existence (hypothetical situation), what will the person observe first,

The gravitational field's absence
The object disappearing (light stops coming)

P.S.- pardon me for the noobness of this question, physics isn't one of my strongest subjects.


texts: I've named a star and would love to be able to find it in the sky - is there an app I can use to locate stars given a specific coordinate?


texts: What is the projection of Earth's axis on the sphere with the Sun in center (see explanation)

texts:
Seems like it is the most convenient SE community for this question..

Imagine the sphere, witch center is the Sun and radius is, say, ~1.5 distance from Sun to earth (in arbitrary time, precise number doesn't matter much).
EDIT: the center of sphere is 'attached' to the Sun.

Then, imagine, the Earth's axis projection on that sphere in time. It leaves some trace.

What will be the picture? Will it repeat itself through some period? What will be the "scansion" for different time periods?

EDIT: as reply to comments I'll add, that my interest is purely out of curiosity, and degree of required accuracy is low. I don't want high precision here, just rough pattern. As I understand this could be done, using mentioned Milankovitch cycles, but I'm not much into mathematics. Though, if I'll not find answer here, I will be forced (by myself) to figure this out, when i'll get some spare time heh.


texts: How can we know that Halley's Comet is going to come again every 76 years? I understand that the comet has an orbit around the sun but how can scientists know that it won't be thrown off course for example by passing Jupiter and Jupiters gravity giving it a tug in a different direction? Its not a very big object in space so it seems to me that its orbit could be changed very easily.


texts: stellarium software: selective artificial satellite display

texts: The Stellarium satellite plugin by default shows all the artificial satellites' orbits around Earth. I’d like to be able to view only certain satellites so that the view is not cluttered with every satellite in existence. Is there a means to create a custom satellite list, or view only relevant satellites?


texts: Is it fruitful to search for a correlation between rates of in-falling matter in black holes and the expansion rate of our universe?

texts:
To my understanding, white holes are hypothetical objects that are time-reversed black holes; black holes gravitationally "suck in" matter whereas white holes "spit" matter back out. As such, I think it's a nice idea that the Big Bang could be the "spitting of matter" via a white hole (assuming such an object exists).

This got me wondering how one could experimentally test for such an object. Since the expansion rate of the universe is increasing, could one possible explanation be that a white hole is continually "spitting out" matter such that an increase of flux of in-falling matter/space could be observed as an increasing rate of expansion of out-pouring matter/space? While I don't know of a way to detect this, I was wondering whether the following idea was fruitful or not.

Given that a supermassive black hole is believed to be at the center of every galaxy, given that most galaxies (sans Andromeda) are receding away at a speed proportional to their distance relative to us observers, and given that the spatial distribution of matter in our universe is isotropic and homogeneous, could one build a simulation of such a concept? To emulate isotropy and homogeneity, one could use a random number generator corresponding to a uniform distribution to place "galaxies" along a grid; accounting for gravitational forces, one can simulate the time-evolution of these galaxies and compare rates of in-falling matter to find a correlation between the rate of in-falling matter and the expansion rate of the universe (likely as a function of time-elapsed, and age and size per black hole). While the simulation does not definitely prove anything, providing a correlation could be interesting in my opinion.

Is this a stupid idea, or is there a potential to build upon this idea? If it is not fruitful, I am curious as to why.


texts: What measures are currently in place to detect asteroids on possible collision courses with earth?

texts: I know some measures must exist, but I have no idea what the programs are, what organizations are involved, or how effective they are.


texts: Why is blue light extincted more strongly than red?

texts: We know that blue light suffers extinction more strongly than red (examples include ISM, atmosphere etc.), but why? Is it a property of the shorter wavelength itself? Can someone provide a conceptual explanation as to why this occurs? TIA


texts: Why do planets tend to rotate in the same direction although they have formed from tumbling asteroids?

texts:
The axial tilts of asteroids seem to vary randomly (let me know if this premise is wrong), while the planets have a strong tendency to rotate in the same way. If planets were formed by colliding asteroids, shouldn't the sum of random tilts result in random planetary rotation? Of course other factors are important, like angle and velocity of impacts, YORP-effect, centrifugal breakup and whatnot, but how could that taken together have any systematic effect on rotation?

Ceres does behave with 4° tilt, but the other of the first discovered asteroids have tilts like 84°, 50°, 42°. Dust particles (and gas molecules if applicable) surely rotate randomly. The Solar nebula had a net spin which gravity and friction has manifested in the orbits of the planets. But shouldn't the netting of rotation be individual for each planet, with uncorrelated tilts, as orbital orientation is for each star?


texts: How could one use the transit of Mercury to try and find the Astronomical Unit?

texts:
I am trying to use the transit of Mercury to estimate the distance between the Earth and the Sun, or 1 AU.

I know that I need to observe mercury from two antipodes, but I do not understand any of the underlying math behind this, or how to derive the astronomical unit from this.

Any help is appreciated!


texts: How bad could we reasonably expect a solar flare to impact earth, and what can be done to mitigate the impact?

texts:
According to numerous articles, solar flares have done damage to the power grid on Earth in the past: http://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/

How bad can we expect a severe solar flare to impact the power grid / electronics?  Would a bad flare also break electronics (e.g. computers), or "just" the power grid?
Is there anything that can be done to reduce the effects?


texts: Any benefit for analyzing the depth of craters across the surface of a planet?

texts: I would like to know what conclusions one could draw from mathematically analyzing the depth of various craters across the surface of a given planet, and then relating that to their position on said planet. Note that I am not looking for immediate conclusions, but rather conclusions that could actually benefit manned exploration in that region. Thanks!


texts:
Is there any popular star or one which we can see with our naked eyes in our milky way that is atleast 90% sun-like(mass,radius,spectra,luminosity).The important thing is it must not be a binary.
Its okay if its not visible to our naked eyes because our sun's absolute magnitude is +4.5!.


texts: If the solar system is nearly flat, then why don't all the planets appear to lie on the same axis when viewed from earth?

texts:
For instance, consider the image below. The location of the planets seem to be so random relative to Earth. If the solar system was indeed flat, then I would expect the planets to lie on the same 'plane', and relative to us, it would look something like the second image. I mean, maybe Jupiter and Mars and Saturn could be on the same plane, but I fail to see how Venus would be.
What is wrong with my understanding here?


texts: Can I sense a bright star pointing an eight foot antenna towards it?

texts:
If I connect an eight foot Yagi or other comparable sized antenna to my oscilloscope and point the antenna at a bright star will I see a voltage on my oscilloscope?

I am not interested in turning the voltage into an image just wondering if I would see a voltage increase when it is on a bright star. I’d like to know your thoughts before I take the time to build the antenna. I’m thinking about in the 25cm range. I’ve heard that’s an active area. My oscilloscope will read down to about 20 millivolts.


texts: Luminosity Schechter function for galaxies

texts:
Just a question I am having trouble understanding. I have the Schechter luminosity function for galaxies, given as:

$$\Phi(L)dL=\Phi_{0}\left({\frac{L}{L_{\star}}}\right)^{\alpha}e^{-\frac{L}{L_{\star}}}\frac{dL}{L_{\star}}$$

I need to consider the case when $\alpha=-1$. And then show that the average luminosity of a galaxy is exactly $L_{\star}$. Could somebody explain how I could go about doing this and perhaps a hint or some part of a setup would be excellent. I really need to understand this.

Another part, which is related to the above question, is asking me to explain why the total luminosity is a finite number, whereas the total number of galaxies diverges. By this does it mean that the total number is infinite? Any extra comments on this would also be really appreciated.


texts: Which Lowell Observatory telescope is this? (used to draw Moon maps for the Apollo program)

texts:
The Fox News article Arizona city played critical role in moon exploration history covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings.

It shows the telescope (shown below) and mentions that it was used to draw lunar maps.

Question: Is it possible to identify which telescope this is exactly? Is there some place where one can read more about it?

click images for full size viewing

  above: Lowell Observatory telescope used by scientists who collaborated with artists to map out the moon for Apollo astronauts (Fox News)

below: Screenshot from July 9, 2019 Fox News video NASA lunar legacy in the Arizona desert


texts:
The third paragraph of the introduction to the ArXiv preprint Constraining Quasar Relativistic Reflection Regions and Spins with Microlensing says:

Quasar microlensing has significantly improved our understanding of the accretion disks (e.g., [five refs]) and non-thermal emission regions (e.g., [seven refs]) of quasars, and the demographics of microlenses in the lens galaxy (e.g., [three refs]) . Since the magnification diverges on the caustics produced by the lensing stars, quasar microlensing can constrain arbitrarily small emission regions if they can be isolated from other emission, in position, velocity, or energy. In particular, microlensing can be used to constrain the spin of black holes by measuring the ISCO size. (emphasis added)

ISCO was previously identified as innermost stable circular orbit.
From what I understand from Wikipedia's Gravitational microlensing; How it works, a microlensing observation records a short term brightening of an object due to focusing by an intervening gravitational body, without useful spatial resolution.
See also the Planetary Society's explanation Microlensing; Beyond our Cosmic Neighborhood
Question: How are microlensing events used to constrain the size of innermost stable circular orbits around spinning black holes? What instruments are used and what kind of analysis is done to obtain a ISCO constraint?

Example light curve of Gravitational Microlensing event - OGLE-2005-BLG-006 Source


texts:
I'm trying to install drizzlepac to follow this tutorial on aligning hst images: https://spacetelescope.github.io/notebooks/notebooks/DrizzlePac/align_to_catalogs/align_to_catalogs.html
However, I get the following errors:
   ERROR: Command errored out with exit status 1:
   command: 'e:\ProgramData\Anaconda3\python.exe' 'e:\ProgramData\Anaconda3\lib\site-packages\pip\_vendor\pep517\_in_process.py' get_requires_for_build_wheel 'C:\Users\FAILTZ~1.DES\AppData\Local\Temp\tmpl00kr2fm'
       cwd: C:\Users\FAILTZ~1.DES\AppData\Local\Temp\pip-install-1l1f4o5x\drizzlepac
  Complete output (26 lines):
  Traceback (most recent call last):
    File "e:\ProgramData\Anaconda3\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 280, in <module>
      main()
    File "e:\ProgramData\Anaconda3\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 263, in main
      json_out['return_val'] = hook(**hook_input['kwargs'])
    File "e:\ProgramData\Anaconda3\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 114, in get_requires_for_build_wheel
      return hook(config_settings)
    File "C:\Users\FAILTZ~1.DES\AppData\Local\Temp\pip-build-env-ey64g5zm\overlay\Lib\site-packages\setuptools\build_meta.py", line 147, in get_requires_for_build_wheel
      config_settings, requirements=['wheel'])
    File "C:\Users\FAILTZ~1.DES\AppData\Local\Temp\pip-build-env-ey64g5zm\overlay\Lib\site-packages\setuptools\build_meta.py", line 127, in _get_build_requires
      self.run_setup()
    File "C:\Users\FAILTZ~1.DES\AppData\Local\Temp\pip-build-env-ey64g5zm\overlay\Lib\site-packages\setuptools\build_meta.py", line 249, in run_setup
      self).run_setup(setup_script=setup_script)
    File "C:\Users\FAILTZ~1.DES\AppData\Local\Temp\pip-build-env-ey64g5zm\overlay\Lib\site-packages\setuptools\build_meta.py", line 142, in run_setup
      exec(compile(code, __file__, 'exec'), locals())
    File "setup.py", line 23, in <module>
      check_call(['git', 'clone', 'https://github.com/spacetelescope/relic.git'])
    File "e:\ProgramData\Anaconda3\lib\subprocess.py", line 358, in check_call
      retcode = call(*popenargs, **kwargs)
    File "e:\ProgramData\Anaconda3\lib\subprocess.py", line 339, in call
      with Popen(*popenargs, **kwargs) as p:
    File "e:\ProgramData\Anaconda3\lib\subprocess.py", line 800, in __init__
      restore_signals, start_new_session)
    File "e:\ProgramData\Anaconda3\lib\subprocess.py", line 1207, in _execute_child
      startupinfo)
  FileNotFoundError: [WinError 2] The system cannot find the file specified
  ----------------------------------------
ERROR: Command errored out with exit status 1: 'e:\ProgramData\Anaconda3\python.exe' 'e:\ProgramData\Anaconda3\lib\site-packages\pip\_vendor\pep517\_in_process.py' get_requires_for_build_wheel 'C:\Users\FAILTZ~1.DES\AppData\Local\Temp\tmpl00kr2fm' Check the logs for full command output.

This was using pip within an anaconda prompt. If I try to use conda, it can't find the package.
I'm extremely new to python, so I'm sure I'm doing something relatively basic wrong! But I've been bashing my head against this for a while.


texts: Accretion of in-falling material for a young main sequence star

texts:
I'm reading material that is seemingly contradictory.  Some sources indicate that the evolution of a protostar to a main sequence star is characterised by a stellar wind that precludes the accretion of further in-falling material.  That is, the (young) star now has a constant mass.  However, other sources suggest that material may continue to accrete for a (brief) period after the protostar has become a main sequence star.

Can someone please confirm the actual process?


texts: If the distance between galaxies is increasing and the speed of light is constant will the most of the light from the universe ever reach us?

texts: Will the light from other galaxies ever reach us if the universe is expanding?


texts: If a giant object would approach the Earth, would Earth start to turn faster or slower while the object starts to become nearer and nearer?

texts:
I am asking myself this question: if a giant celestial object would approach the Earth, would Earth start to turn faster (then day duration would be diminished) or slower (day duration increased) while the object starts to become nearer and nearer?
Thank you!


texts: What makes a flying object keep moving with the Earth's rotation?

texts: When a bird is flying or when a copter is hovering or a plane is flying what force is making them rotate with the earth beneath them?


texts: What are the color progression of a typical sunrise?

texts:
"Dawn simulators" are used to simulate a natural sunrise, or at least the physiological effects of one.

What temporal sequence of color values (e.g., hue, saturation, brightness, and timing) corresponds to a typical spring or summer sunrise? Are the methods for calculating changes in these values based on season?


texts: How does a planet-sized robot standing on a planet affect its gravity?

texts:
I originally asked this at the sci-fi exchange but was told it was off-topic as it was about real-world science.
Here is a picture of Unicron standing on top of the planet Cybertron, as written by Simon Furman and drawn by Geoff Senior in issue #75 of the Transformers comic.
Notice how Unicron is pretty much as tall of the planet's diameter. Assuming he was able to land there without causing the entire planet and himself to explode, wouldn't this have affected the planet's gravitational forces and possibly thrown it off its orbit?


texts: How is phase defined in a binary orbit with eccentricity?

texts:
Are orbital phases of the black spot in the figure measured from some angle or time/period?
Usually, how is phase=0 defined? It is relative to the line of apses perhaps with phase=0 at periastron?
Any of the anomalies below is defined as orbital phase? Please specify reference papers or books.
E: eccentric anomaly
M: mean anomaly
u: true anomaly

Source


texts: Black hole is the densest .... in universe. We know that dimension of universe is 4D . So, what is the dimensions of black hole? Is string theory explains what is it's dimension?


texts: Can you explain the pattern of Hill sphere sizes of the objects of the Solar system?

texts:
I found this image on calculations of Hill sphere for planets/dwarf planets of the Solar system.

 From http://en.wikipedia.org/wiki/File:Hill_sphere_of_the_planets.png

I found it interesting that variation of Hill sphere is intuitive for the first five planets, as the variation is similar to variation of mass/radius of those planets. Mercury has the smallest Hill sphere, Venus/Earth/Mars quite similar, and a giant leap from Mars to Jupiter.

But, Saturn has its Hill sphere bigger than Jupiter, even it is smaller than Jupiter. and this anomaly continues to Uranus and Neptune: They have progressively larger Hill spheres.

And Hill spheres of Pluto and Eris are quite larger than Mercury, Venus, Earth, and Mars.

This was quite surprising for me. Could someone explain why this—for the lack of a better word—anomalies are there?


texts: Why is the Innermost Stable Circular Orbit (ISCO) of a non-rotating black-hole 3 times the Schwarzschild radius?

texts: If anyone has a derivation of this result, it would be appreciated greatly.


texts: A few days ago I saw more than 50 stars moving in a group at night in SW of Florida, what this could be satellites or something else?


texts: Why when we look through a telescope in space, do the billions of stars not block our view from seeing further?

texts:
I know that we are able to "see back into time" by looking very far away through telescopes such as the Hubble telescope, but my question is, wouldn't you run into at least a couple of stars that were blocking your vision when you were trying to look even farther?

Imagine a big Boulder in front of another smaller Boulder  and if we are looking from the side of the larger Boulder, we wouldn't be able to see the smaller one because the bigger one was in the way. Hopefully that simplifies my question. If it is as simple as that, wouldn't we miss stars and not be able to view them?


texts: Why would there be no day/night cycle even though the firmament would still be rotating, according to Copernicus

texts:
In chapter 6 of "The Revolutions of the Heavenly Spheres" where Copernicus maintains that the heavens are immense compared to the size of the Earth, the Edward Rosen translation of the book states this

  "The upshot of the argument, then, is the claim that the earth as a part of the
  celestial sphere shares in the same nature and movement so that, being close to the
  center, it has a slight motion. Therefore, being a body and not the center, it too will
  describe arcs like those of a celestial circle, though smaller, in the same time. The
  falsity of this contention is clearer than daylight. For it would always have to be
  noon in one place, and always midnight in another, so that the daily risings and
  settings could not take place, since the motion of the whole and the part would be
  one and inseparable."
  To add context. Copernicus is debating the classical point which assumes that "the center is at rest, and the nearer an object is to the center, the slower its motion." Copernicus in the previous paragraph states that this assertion could be translated into a sphere. Where the center are the poles, and the constellations around those poles (i.e. Ursa Minor, Draco, etc...) would be rotating slower as they are closer to those poles. Yet Copernicus refutes this by saying that if those constellations truly moved slower than the rest, they wouldn't be able to make a full 360° rotation in a year.

Copernicus then in the paragraph above, argues that the Earth too must orbit around the center in order to account for the "slowness" in the poles. However Copernicus further refutes this by stating that there would be no day/night cycle in this case.

To elaborate on my question asked in the title. Why would the Earth need to orbit in order to account for this "slowness." And why would there be no day/night cycle even though the firmament would be rotating and not the Earth along with it.


texts: How to distinguish primary hosts (stars) and orbiting satellites (planets) and tertiary bodies (moons) by their mass and trajectory?

texts:
Suppose one has run a gravitational simulation of N bodies (has the mass, vector positions, vector velocities, etc for each body), but knows nothing a priori about the system (ie, one does not know anything regarding composition, or which bodies are stars or planets). I would like to use the simulation results to categorize which bodies are primary hosts and which ones are satellites (and if possible, which "tertiary" bodies are orbiting the satellites). Is there a way to create a hierarchy that identifies whether a body is a primary host or satellite or tertiary? I would like to find a method of doing this such that the method can be applied to cases for N > 10^3 bodies.
For context, consider a 9-body system like a simplified example of our solar system (8 planets + 1 star). One can identify the Sun as the only primary host and the planets as the satellites because the ratio of the mass of the Sun to the mass of Jupiter (most massive planet of our solar system) is 1048. One could also use the approach of noticing that the center of mass would be inside of the Sun (or very close to in a point-mass simulation). But, the center of mass approach only works for nearly circular stable orbits around a single host; for unstable orbits, a body can deviate from its tangential path about the center of mass.
If we consider a binary star system for which both stars are of comparable mass, then I think that the ratio of the mass of any single host star to the mass of the most massive planet orbiting this binary star system can decrease; in other words, for each primary host body added to a system, the combined gravitational force at certain points in the orbit required to keep a satellite body in orbit should decrease if the system is stable, thereby decreasing the ratio of the mass of any host body to the mass of the most massive satellite body. (I suppose the same logic could be extended to host planets and satellite moons, though I suspect the ratio of masses would decrease; would this logic also apply to unstable orbits?)
Is this line of thinking correct? More importantly, what is the right way to think about this?


texts: Observed sun/moon rise/set times to nearest second?

texts:
Where can I find a list of observed (not computed) sun/moon rise/set
times to the nearest second, along with the location (latitude,
longitude, altitude [or enough information to find these three
values]) and, ideally, weather conditions (temperature/pressure)?

Since it's hard to tell where the "middle" of the sun/moon is when
it's setting, these would be the setting times for the lower or upper
limb of the sun/moon.

Reason: I'm trying to compute sun/moon rise/set to the nearest second
using high-precision data, and I'm curious to see if I can get
anywhere near the actual observed time. My technique:

Use NASA's Chebyshev approximations to find the positions of the
Sun and center of the Earth.
Use an elliptical (not spherical) model of the Earth to find the
ICRF xyz coordinates of a given location at a given time. This
includes compensating for altitude and precession.
Model refraction based on weather conditions, including adjusting pressure for altitude (weather stations report air pressure normalized to sea level, which isn't the same as actual air pressure, especially at higher altitudes).

I realize down-to-the-second computations of sun/moon rise/set are
probably impossible, in part because refraction depends on more than
just local conditions, but I'm curious to try.


texts: Is it true that we see the center of the milky-way for only half of the year?

texts:
I'm not an astronomer, please excuse my non-formal language.
Since we are located in one of the arms of the Milky way, the center of the galaxy should be in one direction from our location, while in the other direction, we stare into the "other side".
So at nights as we are in the orbit area that is between the sun and the center of the galaxy we are able to see the center (the "milky-way"), while when in the other side of the orbit, at nights, we are not able to see it.
Does this mean we only see the milky way (meaning the milky-way's famous pattern) half of the year?
In the below diagram, the small circle is our year-orbit around our sun. Red dot is the earth location on day 0 of the year and the green dot is the earth location on day 180th of the year.
I know that as we are orbiting our sun, it also orbits the galaxy, but since it is so slow, it is negligible for this questions.

Is this reasonable?
I mean, if we look at the sky, we will see the center of the galaxy only during half of the year?


texts:
I don't know much about astronomy, but my kids are asking for telescopes to view planets, stars etc. Could anyone tell me if this Eduscience telescope is any good?

  This kit contains a 40x with a 41cm body, 20x 30x 40x eyepiece, a diagonal mirror, 30mm diameter objective lens and tripod.

  Size H51, W44cm.


texts: I am in Northampton England and every night in the SW sky is a very bright, white light that twinkles. It visibly appears to be moving towards the west but appears pretty much the same start place every night. Could anyone possibly tell me what it might be please?


texts:
In an answer on a different SE someone raised the point that “common” explainations published never discuss stars being captured.  Presumably binaries are formed as pairs, or team up while still in the birth cluster.

It seems quite plausible that an aged star (or stellar reminant) can be paired with a main sequence star in its prime, having paired up well after the old supernova was completed.

Is this mechanism of multi-body reassortment known to occur, presumed, or thought to not occur?

Another mechanism implied but not detailed in popular works is the possible situation with Proxima Centauri: a star going with the flow in the galaxy may find itself loosly attached to another star (or system), and this bond is so tenuous that it can easily be broken by another passing star, so the distant star do-si-dos to different partners over the course of billions of years.  Is this an accurate depiction of the real situation?  This loose attachment out of the general flow can occur with stars of any mass, right?

In any case, a star can be captured with planets, right?  Naturally a close-enough encounter between stars (and reminants) could seriously disrupt a planetary system, but I want to check on the possibility that capture with planets is also a possibility.  I think that’s not a problem for the “loose attachment” case, and Proxima Cen may indeed have a planet.  How about the necessary mechanics of binary reassortment?  Is that necessarily so close and tight thatbplanets would be seriously disrupted, or is it plausible that planets would simply go along for the ride?

Update: PSR B1620-26.  A neutron star captures a star with planet, trading off its original companion.


texts: Why do scientists think life requires water?

texts:
As far as I know, scientists seeking extraterrestial life are simply looking for plantets containing water in liquid state. To be honest, I find this weird.

It is true that life - in the form we know on Earth - cannot exists without water. But how can one proof that such life isn't but a special case out of a bunch of other different types of life?

Actually, I think we can come out with at least one example of a "organism-like thingy" that would not require liquid water. Well, we could build a simple robot, whose "natural ecosystem" would be a junkyard (for mechanical, electric and electronic garbage). That robot would would fuel itself with solar energy, and reproduce by seeking out appropiate parts in the junkyard and building a copy of itself from them. Of course, that's just a theoretical example, I know it has many faoults, but I still hope the idea is clear - it should be indeed possible for life to exists without water.

I have also heard (sorry, I can't remember the source) that theoretically, there could be an organism whose metabolism would rely on sulphur.

So, unless scientists can proove that no life can exists without water (any life; not just Earth-like life), why do they keep looking just for water?

Unless, of course, we define "life" as "any organism functioning like Earth organisms; therefore, metabolising organic structures with enzymes, built of protein, requiring water, etc"

BTW. This question is a little bit different than Why is liquid water considered a requirement for life? . The answers there were pointing out that water is a good solvent. And I'm (also) asking why is any similar solvent considered needed. See my example above.


texts:
How can I calculate position (alt, az) of star for observer at some station (longitude, latitude) on specific date and time? I need full coordinates reduction with all elements included in calculation (proper motion of star, atmospheric pressure and temperature... )

I tried with pyephem but I am not sure can I finish.

import ephem

polaris = ephem.readdb("Polaris,f|M|F7,2:31:48.704,89:15:50.72,2.02,1")

polaris.compute('2016/3/1 16:22:56')

print polaris.a_ra
print polaris.a_dec

I also tried with astroplan and I think that I am closer to solution, but still don't know how to get coordinates after reduction and add proper motion.

import astropy.units as u
from astropy.coordinates import EarthLocation
from astropy.coordinates import SkyCoord
from pytz import timezone
from astroplan import Observer
from astropy.time import Time
from astroplan import FixedTarget
import numpy as np
import astropy.units as u
from astroplan.plots import plot_sky
from astroplan.plots import plot_parallactic
from astroplan.plots import plot_airmass
import matplotlib.pyplot as plt
from astroplan import FixedTarget

longitude = '21d33m20.4s'
latitude = '+43d08m24.6s'
elevation = 1150 * u.m
time = Time('2015-06-16 12:00:00')

location = EarthLocation.from_geodetic(longitude, latitude, elevation)

observer = Observer(name='Name',
               location=location,
               pressure=0.615 * u.bar,
               relative_humidity=0.11,
               temperature=0 * u.deg_C,
               timezone=timezone('Europe/Belgrade'),
               description="..")

coordinates = SkyCoord('2h31m48.704s', '89d15m50.72s', frame = 'icrs')
polaris = FixedTarget(name='Polaris', coord=coordinates)

plot_airmass(polaris, observer, time)

ax = plt.gca()
box = ax.get_position()
ax.set_position([box.x0, box.y0, box.width * 0.8, box.height * 0.8])

plt.legend(loc=1, bbox_to_anchor=(1.35, 1))
plt.show()


texts: Calculate eclipse days and duration of satellite

texts:
If a satellite is revolving in a GEO orbit, then what will be the eclipse duration for it? How to calculate when the satellite will enter the dark side of the Earth?

Any formula or online tool would be appreciated.


texts:
Bear with me. I want to explain this to my 6 and half year old.

If, all things being equal, we could reach out to the Sun with a suitable implement, a gigantic space knife, could we cut a piece off the Sun? Take a slice from it? Do we end up with a body of Hydrogen and Helium, or is it impossible to extract anything from it?

I know that the Sun is a massive ball of plasma, the sheer mass compressing the gas through gravity until fusion is achieved. What I have been asked is, effectively, what happens if you try to take a piece of that plasma? Of our sun?


texts:
I'm new here this is my first question. I'm an engineering student and I really like mathematics, I've recently watched a movie about Stephen Hawking (The Theory of Everything) In which he makes various discoveries about black holes. This made me curious about cosmology and the only thing I know about this subject is

Cosmology is a branch of astronomy concerned with the studies of the origin and evolution of the universe, from the Big Bang to today and on into the future

This made me question how accurate it is, since there is no way to see


texts: Stellar Aberration and Lorentz Transformation

texts:
The aberration of starlight is claimed to result from the Lorentz transformation of Special Relativity, but I am having problems to understand this.  Assume we have two reference frames $x,y,z$ (the reference frame of the star) and $x',y',z'$ (the reference frame of the observer (assumed to be located on the $z'$ axis)). Both reference frames move with constant velocity $v$ relative to each other along their $x$ axes. At $t=t'=0$ the origin of both reference frames shall coincide and at this moment a light ray sent out along the $z$ axis i.e. along
$$x=0$$
$$y=0$$
$$z=ct$$
According to the Lorentz transformation
$$x'=\gamma (x-vt)$$
$$y'=y$$
$$z'=z$$
$$t'=\gamma (t-vx/c^2)$$
this light ray travels in the observer's reference frame along the coordinates
$$x'=-\gamma vt=-vt'$$
$$y'=y=0$$
$$z'=z=ct=ct'/\gamma$$
This is generally interpreted to the effect that the apparent position of the star shifts by an angle $\alpha$ where
$$tan(\alpha)=(-x')/z'=\gamma v/c$$
However, the star emits light rays in all directions, therefore also in the direction
$$x=vt$$
$$y=0$$
$$z=ct/\gamma$$
and this ray travels in the observer's frame along
$$x'=0$$
$$y'=0$$
$$z'=z=ct/\gamma=ct'$$
The observer on the $z'$ axis sees the star therefore exactly at the origin i.e. the same position as for the stationary case. The only difference is that the star appears to be rotated about its axis, but there should not be any positional change of the star due to this.
Is there any way to resolve this apparent contradiction?


texts:
So I was watching something that said

if we compressed Earth into the size of a peanut: we would get a black hole;
if we compressed Mount Everest into a few nano-meters; we would get a black hole.

Can I make a black hole with one or two atoms? If yes, would it become larger and turn into normal-sized black hole?


texts:
IC 1101 is the single largest galaxy that has ever been found in the observable universe, but does IC 1101 have any other name or at least a nick-name, perhaps something more soothing to the ear and easier to remember?
Many times notable objects receive additional names besides those entered in catalogs of objects. Since IC 1101 "the biggest", I'm wondering if it's been singled out and given another name.
N.B. I know in future another galaxy will be discovered bigger than this. But I don't mind giving a good name to that also.


texts: Broadband spectrum is one which is inclusive of all the observed wavelength ranges. In the case of the BB spectra of our Sun, there is a sharp (non-differentiable) kink in the curve in the UV-range (as shown above). What is the significance of this kink?


texts: A [very basic?] question about light scattering and colors

texts:
Since the night two days ago, the moon here in Israel appears to be orange as it rises, and then gradually becomes white as it continues travelling across the sky.

This phenomenon comes in a great timing as I am starting to become interested in astronomy (I have no special knowledge in astronomy, just to make it clear).
So I googled up and came across this explanation.
I'll try to summarize: it says that it happens because of Earth's atmosphere, that tends to scatter short wave-lengths (such as blue and green) and let long wave-lengths (such as red and orange) pass through. When the moon rises, it's in the position where the light coming from it to our eyes goes through the thickest layer of atmosphere (as opposed to when it's high up in the night skies) and that gives the orange effect.
I totally get this explanation, but it raises a couple of questions for me, whose answers I couldn't find. Maybe you could help me out.

Why doesn't the orange moon phenomenon occur all the time?
It does not happen quite often. What's so special about the past three nights? I mean, the rising moon's light always has to go through a thick atmosphere layer, doesn't it?
Maybe that's not entirely astronomic, but, to complete the big picture - why does our atmosphere scatter short wave-lengths?
This explanation suggests that all light coming to us from the sun is (at least) slightly reddish. Is this measurable (if true)? Because to the naked eye, sunlight refrected through a prism shows no tendency towards red.

Thank you for your time reading the question, I hope you could rescue me from my ignorance...


texts: What is a black hole's "shadow" and the best angle to view it to measure the spin?

texts:
This excellent answer mentions several ways to try to observationally measure the spin of a rotating black hole. The third one is intriguing, but I don't understand how this works:

  The spin of a black hole also affects how it deflects light. Consequently, the pictures of a black hole's shadow such as taken by the event horizon telescope can be used to determine the spin of the black hole (if we happen to view it under the right angle).

Question: What is a black hole's "shadow" and the best angle to view it to measure the BH's spin?


texts: Why is there no time in the distance equation using Hubble constant, red shift and speed of light?

texts:
So I had some problem and I think I solved it, then I began to dig out things around it and I found some equations using red shift etc. to get speed of the object in Universe relative to us and then I found this one:

distance=speed of light/Hubble constant*red shift

It took some time before I found the thing which seems to be wrong with this thing.
How can I get the distance traveled if there is no time mentioned?
Thanks in advance!


texts: Effect of particulates on the visibility of stars?

texts:
I am looking for a (mathematical) relationship - either empirical or theoretical - which quantifies how the visibility of celestrial objects decreases with increasing amount of particulates in the air. I would be already happy if somebody knows such a relationship for the atmospheric light attenuation effects of black carbon or soot. Those two are actually not the same as Alfred Wiedensohler from the Leibniz Institute for Tropospheric Research points out in a presentation on the topic:

Soot is carbon particles resulting from the incomplete combustion of hydrocarbons. Soot contains polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Black carbon (BC) itself is neither a toxic nor a carcinogen.

What I expect (but I am happy to be proven wrong) is that I am actually after the three constants in the following expression:
$$ f_{\rm attenuation}(d) =  \frac{1}{k_c + k_l \cdot d + k_q \cdot d^2}$$
In this formula, $d$ is the distance between the light source and the observers, so in our case it would be the height of Earth's atmosphere (if we assume homogenous distribution of soot/ BC over the air column).
$k_c$ is called the constant attenuation factor, $k_l$ is the linear attenuation factor, and $k_q$ stands for quadratic attenuation factor.
Such an expression would already be very helpful, but if there is science on the overall effect of particulates, that would be much cooler. I am dreaming of having a formula for visible magnitude of stars with naked eye in dependence of particulate concentration (for ideal, pitch-black nights without clouds).
Background
My question is inspired by What effect do aircraft have on night-time visibility? which does not have an answer yet.
I am aware that in the physical oceanography and in marine biology, there are extensive studies on light attenuation due to BC or other dissolved substances in water, and most search results are on that.
References and related questions

C.Liousse, H.Cachier, S.G.Jennings: Optical and thermal measurements of black carbon aerosol content in different environments: Variation of the specific attenuation cross-section (1993)
H. Horovath: Atmospheric light absorption — A review
(1993)
ESA on Desert dust plume over the Atlantic observed by Aeolus and Sentinel-5P


texts:
A meteor recently flashed over Queenland.

The meteor has been described by various people as appearing cyan or aqua, so the blueness of the image can't be due to a camera issue. The colour doesn't appear to be anything found along the black body spectrum either.

What (chemical/physical process) would cause this meteor to appear cyan?

 click for full size, Source

  ‘I saw it come right down in the sky’: the meteor over south-east Queensland on Saturday night. Photograph: Craig Turton/AAP


texts: Is there a minimum size for a galaxy to have spiral arms?

texts:
Is there a minimum size or mass for a galaxy to present spiral arms? I don't remember many small galaxies with spiral arms.

Does the mechanism responsible for producing spiral arms no longer hold if the galaxy is too small?


texts: Why is today the shortest day but the solstice is actually tomorrow?

texts: Here in Ashland, Oregon, today (Dec 20, 2020) is the shortest day length of the year at 9:05:45.  But the winter solstice isn't until 2:02 AM PST tomorrow (Dec 21, 2020). Tomorrow's day length is a whopping three seconds longer at 9:05:48.  Why is tomorrow's day length greater than today? It would seem to me that tomorrow's sunrise and sunset are slightly closer to the magic moment of winter solstice and should therefore account for a slightly shorter day.


texts:
I was going through the official SETI website, when I came across this article on the same website which said :

Today, the SETI Institute uses a specially designed instrument for its SETI efforts – the Allen Telescope Array (ATA) located in the Cascade Mountains of California. The ATA is embarking upon a two-year survey of tens of thousands of red dwarf stars, which have many characteristics that make them prime locales in the search for intelligent life.

The part that I was not able to understand was :  The ATA is embarking upon a two-year survey of tens of thousands of red dwarf stars, which have many characteristics that make them prime locales in the search for intelligent life.
So my question is : Why is the SETI survey limited to only Red Dwarf Stars? Is there something special about them that I seem to be missing?
Also, is this survey still active?


texts: How does the Moon move in the "night" sky as seen from the poles?

texts:
A photo in the NYTimes article Ice Surveys and Neckties at Dinner: Here’s Life at an Arctic Outpost has got me thinking.

During the winter months at either the north or south pole, when it is constantly dark, how does the Moon behave?

Would a nearly-full moon sometimes circle for days without setting, or would it still rise and set, or would it be all together missing, or some combination of all of the above?


texts: Did uncertainty principle triggered big bang?

texts:
So i want to know why world changed from the empty state ( no materials, energy and ...) from to the it's staring state in the big bang shape?

based of this answer's to this question:
big-bang-thoery-what-triggered-it-and-why
they said:

  You may think of the pre-Planck and the Planck epoch as a state of the
  universe, which is dominated by quantum fluctuations. They don't need
  a reason or a cause to occur. They are a consequence of Heisenberg's
  uncertainty principle.

So,Did any law like uncertainty principle caused this to be happened or any somethings?

Or

This is one meaningless question?!!!

Thanks a lot.


texts:
Dr. Avi Loeb, the distinguished astrophysicist and chair of Harvard's Astronomy Program, just published a book called Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.
In the book, Dr. Loeb calls out several specific peculiarities about the interstellar object Oumuamua. He proposes a rather shocking hypothesis:

I submit that the simplest explanation for these peculiarities is that
the object was created by an intelligent civilization not of this
Earth.

In interviews 1, 2, 3: Dr. Loeb mentions several peculiarities.  Here are three:

Oumuamua has a unique light curve.  Uhoh has a nice analysis and some great graphics in this answer: Could asteroid 'Oumuamua actually be round?. Dr. Loeb claims that the high aspect ratio implies this is not a natural object. He uses an analogy of a thin piece of paper falling through the air having a less extreme aspect ratio.

Oumuamua showed acceleration unaccounted for by orbital mechanics after its close pass to the Sun similar to a comet.  A comet gets its push due to evaporation of gasses, but there was no evidence that Oumuamua had a tail of gas.  Dr. Loeb proposes that Oumuamua may have been designed as a light sail.

Dr. Loeb claims Oumuamua's velocity as it entered the Solar System is slower than 1 out of 500 near star systems in an LSR reference frame.

Does the evidence support Dr. Loeb's hypothesis that Oumuamua is most likely of extra-terrestrial origin?


texts: GPU-based astronomical software for MacOS/AMD/OpenCL environment

texts:
I notice that most astronomical software that uses GPUs to accelerate computation makes use of Nvidia's CUDA toolkit. Are there established software packages that, instead, can be used on a modern Mac with an AMD GPU and the OpenCL GPGPU environment?

I'm specifically looking for transient detection and pulsar search tools (radio astronomy). Bonus points if they are open source.


texts: Software apps for calculating distances between planets

texts: Are there somewhere any software apps for calculating distances between any planets in our solar system?


texts: Can rogue/nomad planets and other starless planetary bodies orbit each other in a stable system?

texts:
Nomad planets (also called planemos or rogues planets) which drift in space without  a star or substellar object to orbit. The majority of such planets we have discovered are gas planets with thick atmospheres and no landmass, although some of them could be frozen deserts with rocky surfaces like Earth's.

Most nomad planets we have found are alone/solitary, and do not orbit any other companion objects. We have only discovered 1 (as in 1.0) binary planemo called 2MASS J11193254–1137466.

What I'm asking here is that can a large system of 6 or 7 rogue planets and other planetary bodies orbit each other and remain stable; basically like a tiny open cluster or huge multiple star system, just comprised of planets instead of stars?


texts: How to install the Barlow lens on this telescope?

texts: I've brought a 4.5inch astronomical telescope recently which has an aperture of 114mm and a focal length of 1000mm, and two eyepieces. The two eyepieces were of 25mm and 10mm. I enjoyed stargazing using the 25mm eyepiece. But the stuff that I could see with my 25mm eyepiece was not visible through the powerful eyepiece. I'll post some pics. Can someone tell me how to install the Barlow lens?


texts: Slow moving star like objects in the night sky

texts: So yesterday at about 2am I was watching the sky when I saw a small star like object moving very slowly across the sky. My initial thought was that it was a satellite due to the fact it was moving so slowly and wasn’t flashing. However  then I saw another one moving in the same direction about 10 minutes later. I had to keep letting my eyes adjust to the darkness to see it as it was so small but in total, I saw 4 of them moving in very similar directions, almost like they were following a path. There was about a 5-10min gap between each one and I could see it the entire time until it dipped over the tree line. I live in a very rural area so there was no light pollution or anything to interfere with the view. Now I know that around about now we are able to observe the Perseid meteor shower from the comet Swift-Tuttle but these object were very slow moving and I don’t really know how slow a meteor can move, but isn’t it strange that all of them were moving in the same direction? I also did see some normal meteors but as you’d expect, they only lasted for a second or under. Anyone have a clue what’s going on? Thanks.


texts: Does the orbits of stars in a binary system have a common focus, which is the center of mass of the stars?

texts:
I know that when a planet orbits a star (and assume the star is stationary because its mass is >> the mass of the planet), the orbit is an ellipse, and the star sits at one of the foci of the ellipse. What I am wondering is if instead of a planet surrounding a star but a binary system where the two stars's mass are of the same order of magnitude, are their orbits ellipses and share a common focus at the center of mass?

Intuitively I think it is true because this is a result generalized from the planet surrounding the star case but strictly speaking I have a hard time to mathematically prove it.


texts: What is main radiative mechanism in Gunn-Peterson effect?

texts:
I'm having a hard time understanding the Gunn-Peterson effect and the Ly-alpha line and I've written a couple of questions below.

The trough we see in the spectra of quasars is the Gunn-Peterson trough, right? Does this trough have to start from the Ly-alpha line?

If neutral hydrogen along the line of sight to the distant quasar is few, do we expect the Ly-alpha forest to be sparse?

What is the main radiative mechanism in the Gunn-Peterson effect?


texts: what should be the minimum magnification of the telescope to see properly the cloud(red spot) of jupiter?

texts: and what should be the minimum focal length of objective lens and focal lens. I've a celestron  which have 300mm focal length of  objective lens and 6/4/12/20 mm of eye piece  but it's hard for me too the jupiter so I asked here "what  should be the minimum magnification of a telescope?"


texts: Does the term "Hydrogen burning" mean the same as "Hydrogen fusing" in astronomy? If not, then what is the product of "Hydrogen burning"? Assume the product of "Hydrogen fusing" is helium.


texts: Could an asteroid impact cause radioactive fallout?

texts:
Could a (regional or global) fallout of radioactive material be a "bonus" disaster effect of an asteroid impact? My reasoning for how such a scenario maybe could be possible:

A) Some asteroids maybe consist of lots of radioactive heavy metals because they were initially formed by ejecta from the cores of planets during planetary collisions. Maybe even an airburst of a rather small such an asteroid could cause widespread dangerous radiak fallout?

As I understand it, Earth's initial uranium has fallen into the core. The uranium mines dig into concentrated deposits of uranium in the crust which came from uranium rich asteroids.

B) If any kind of asteroid large enough hits a uranium rich part of the Earth crust (making it the second one on the same spot), it could maybe eject much of Earth's own uranium and thus cause a dangerous fallout?


texts: How does one find the extinction coefficient of a particular galaxy?

texts: I am doing photometry on a number of objects in a number of different galaxies. I need the extinction coefficients for these galaxies for various filters passes. Is there some database that displays extinction values for different galaxies at different filter passes?


texts: When I listen to the Planetary Radio podcast, there is a section at the end where they suggest objects to look out for in the night sky. If I am in the UK, but they are talking about the USA, will I still be able to find the objects they are referring to?


texts: Can I see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50?

texts:
Is it possible to see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50? And even the moon?
This is the description of the telescope:

User-friendly and easy to install with magnification up to 100x.
A telescope is a learning and discovery tool that is suitable for both old and young. This model is larger and has significantly better optics than the telescope that Galileo Galilei used during his astronomical discoveries hundreds of years ago. Magnifies from 30-100x. The viewfinder binoculars (5x24 mm) make it easy to roughly calibrate the telescope and the stand is easy to mount. Focal length 600 mm. Light opening 50 mm. Weight about 3.1 kg. Live incl. 2 eyepieces.**